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Greeting everyone,
I have the 1995 Volvo 940 non-turbo fuel sending unit out of the tank to install a new Bosch motor. The two wiring from sending unit going down toward the pump measure 1.5mm (AWG # 14) in diameter. The wiring pigtail harness from the fuel pump measure 2.5mm in diameter (AWG #10). I need to splice the two different size wiring and I am concerned about if that is the correct way to do it. Is it safe to do this? I very much appreciate any thoughts you may have concerning this issue.
Best,
Habib.
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Dear Habib,
Hope you're well and stay so. When I replaced my '95 940's fuel pump, it was factory-installed on the send unit. There was no wiring "pig tail". The wires from the send unit attached directly to the fuel pump's contacts.
If: (a) the wires from your send unit are long enough to reach the fuel pump's contacts and (b) the fuel pump's pigtail wires are soldered to the motor's contacts, I'd remove the pigtail wires and solder to the pump's contacts, the wires from the send unit. If I recall correctly, those wires are pink and gray.
If the wires from the send unit are not long enough to reach the pump's contacts, then I'd slide heat shrink tube over each of the pigtail wires, and then solder to each pigtail wire, one wire from the send unit. Be sure to use rosin-core solder, not standard (acid-core) plumbing solder.
Rosin-core solder will make a very strong connection. I'd then slide the heat shrink tube over solder joint and shrink the tubing.
I'd not use crimp-type connectors to join the wires, because the wire sizes are too far apart. One might "get away" with a crimp join between #12 and #14 wires.
I'm surprised that #10 wire is present. In U.S. homes, use of #14 wire - rated for 15 Amps - is standard for most circuits. No. 14 wire can handle loads up to 12 Amps (20% less than the maximum rating).
In a U.S. home, #12 wire would be used for circuits in a kitchen or a laundry room. A #10 wire - rated for 30 Amps - in a U.S. home would be used only for heavy-duty appliances, e.g., a large window air-conditioner or perhaps a convection oven.
Thus, use of #10 wire on an auto fuel pump - when the motor draws only 6.5 Amps - seems unusual and unnecessary.
Hope this helps.
Yours faithfully,
Spook
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Dear Spook. If you look in engineering tables, stranded copper wire such as used in auto applications (called primary wire) can handle only about 1/3rd the current as the same gauge of solid core copper wire used in household AC wiring (Loomex). The minimum gauge needed for a given circuit amperage also depends on the total run length, voltage and acceptable voltage drop. In a 12V 15A circuit application such as the fuel pump, which is constantly running at say 7-12 amps (depending on whether it's a Regina or Bosch system pump and how badly worn it is), although 16 gauge is listed as the technical minimum in engineering tables, 14 gauge is what you would normally want to use, 12 gauge is playing it more than safe and 10 gauge is overkill as you note.
While I'm on the topic of wire sizing, although going with a thicker gauge wire is better for handling current and is less susceptible to physical damage or losing a strand or two when the insulation is being stripped, that's not always the better option. When flexing (which includes vibration) is an issue then you want to go with smaller gauge thinner wire, more specifically thinner strands, which means more strands if you're getting close to the current limit . Flexing will harden copper until it eventually fractures. The fatter the strands, the faster it hardens and breaks (we would never use solid core household wiring with a kettle, let alone a lamp). Nine times out of ten when someone here says their power windows aren't working we know it's a broken wire at the hinge, so there's an application where Volvo under-engineered and should have used a smaller gauge or higher strand count wire. Test lead wire, which you can buy in bulk in red and black, would be better for repairs there. Another weak spot is at the 240 tailgate hinges, but Volvo actually did use smaller gauge, higher strand count wire as well as molded vinyl reinforcing, but it still can only last so long. Using standard primary wire there wouldn't last anywhere near as long, as anyone can attest who attempted to try use everyday cheap wire there. Cheaper aftermarket harnesses may or may not last as long as the Volvo harness depending on the type and quality of wire they use.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now
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Dear Spook,
Thank you so very much for your time and suggestion. To be safe, I managed to disconnect and remove the extended Walbro fuel pump wire harness off the pump and since there was an adequate length of factory red and black wires on the sender unit, I installed terminal connector on them, placed them in the socket, and insert the socket onto the fuel pump and it turned out perfect.
Again, thank you for your time responding to my post.
Best,
Habib
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Dear Dave Stevens,
Hope you're well. Thank you, Sir!!!, for your comments. I'm not an electrical engineer and the World surely is better for that!
All of the wire in 940s - so near as I can tell - is stranded, so there was no reason to address conductor format (stranded vs. solid).
There was a reason to address large differences in wire diameter. There surely are crimps intended to join wires of different weights. But I didn't want to task Habib with finding such items in a time of scarcity of common items. I do not know where he hangs his hat, so have no idea what things he may be able to get.
So, I thought it best to recommend use of solder to ensure a strong and durable joint.
Hope this helps.
Stay safe and well!!
Yours faithfully,
Spook
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